Despite our best efforts to roll out mother-to-child HIV prevention services, many children in developing nations such as Zambia do not escape infection. Fortunately, life-saving antiretroviral therapy is now available in many settings, but i order for it to work, infected newborns must be identified and treatment started immediately. Diagnosis of infant HIV infection represents a major hurdle to this process. Unlike HIV testing in adults, infant diagnosis requires special laboratory equipment and personnel available only in sophisticated laboratories. As a result, most children either have no access to HIV diagnosis at all or must wait for weeks to receive their test result. In Zambia - as in many countries in the region - more than half of newborns who are tested and found to be infected never actually start treatment. The University of Cambridge has developed a new point-of-care (POC) test called SAMBA that can diagnose infant HIV infection by detecting HIV genetic material in the blood. Designed specifically for developing world settings, SAMBA results are ready in two hours. Two versions of the test are available, a qualitative test (for infant diagnosis) and a semi-quantitatie test (for treatment monitoring). This proposal describes a cluster-randomized trial of the SAMBA POC virologic test to improve outcomes of HIV-infected children in Zambia. The POC technology will be placed in primary care sites and serve two functions: (1) provision of same-day, early infant HIV diagnosis at 6 weeks of life for infants born to HIV-infected mothers, and (2) treatment monitoring of children on antiretroviral therapy. Twelve facilities will participate n the trial. Half of the sites will be randomly assigned to implement the POC technology and the other half will employ the current standard of care - where infant diagnosis is performed off site and treatment monitoring is based primarily upon clinical assessment. The trial's primary outcome will be the proportion of HIV-infected children in each study arm who remain alive, in care, and with no HIV circulating in their bloodstream (an indicator of treatment success) 18 months after their initial diagnosis. The study will be conducted by the Centre for Infectious Disease Research in Zambia (CIDRZ). Established in 2001, and led by the team proposing this study, CIDRZ has substantial experience with both NIH-sponsored research and PEPFAR-sponsored service implementation.